Wafer level phosphor coating method and devices fabricated utilizing method

ABSTRACT

Methods for fabricating light emitting diode (LED) chips comprising providing a plurality of LEDs typically on a substrate. Pedestals are deposited on the LEDs with each of the pedestals in electrical contact with one of the LEDs. A coating is formed over the LEDs with the coating burying at least some of the pedestals. The coating is then planarized to expose at least some of the buried pedestals while leaving at least some of said coating on said LEDs. The exposed pedestals can then be contacted such as by wire bonds. The present invention discloses similar methods used for fabricating LED chips having LEDs that are flip-chip bonded on a carrier substrate and for fabricating other semiconductor devices. LED chip wafers and LED chips are also disclosed that are fabricated using the disclosed methods.

This invention was made with Government support under Contract USAF05-2-5507. The Government has certain rights in this invention

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to methods for fabricating semiconductor devicesand in particular methods for wafer level coating of light emittingdiodes.

2. Description of the Related Art

Light emitting diodes (LED or LEDs) are solid state devices that convertelectric energy to light, and generally comprise one or more activelayers of semiconductor material sandwiched between oppositely dopedlayers. When a bias is applied across the doped layers, holes andelectrons are injected into the active layer where they recombine togenerate light. Light is emitted from the active layer and from allsurfaces of the LED.

Conventional LEDs cannot generate white light from their active layers.Light from a blue emitting LED has been converted to white light bysurrounding the LED with a yellow phosphor, polymer or dye, with atypical phosphor being cerium-doped yttrium aluminum garnet (Ce:YAG).[See Nichia Corp. white LED, Part No. NSPW300BS, NSPW312BS, etc.; Seealso U.S. Pat. No. 5,959,316 to Lowrey, “Multiple Encapsulation ofPhosphor-LED Devices”]. The surrounding phosphor material “downconverts”the wavelength of some of the LED's blue light, changing its color toyellow. Some of the blue light passes through the phosphor without beingchanged while a substantial portion of the light is downconverted toyellow. The LED emits both blue and yellow light, which combine toprovide a white light. In another approach light from a violet orultraviolet emitting LED has been converted to white light bysurrounding the LED with multicolor phosphors or dyes.

One conventional method for coating an LED with a phosphor layerutilizes a syringe or nozzle for injecting a phosphor mixed with epoxyresin or silicone polymers over the LED. Using this method, however, itcan be difficult to control the phosphor layer's geometry and thickness.As a result, light emitting from the LED at different angles can passthrough different amounts of conversion material, which can result in anLED with non-uniform color temperature as a function of viewing angle.Because the geometry and thickness is hard to control, it can also bedifficult to consistently reproduce LEDs with the same or similaremission characteristics.

Another conventional method for coating an LED is by stencil printing,which is described in European Patent Application EP 1198016 A2 toLowery. Multiple light emitting semiconductor devices are arranged on asubstrate with a desired distance between adjacent LEDs. The stencil isprovided having openings that align with the LEDs, with the holes beingslightly larger than the LEDs and the stencil being thicker than theLEDs. A stencil is positioned on the substrate with each of the LEDslocated within a respective opening in the stencil. A composition isthen deposited in the stencil openings, covering the LEDs, with atypical composition being a phosphor in a silicone polymer that can becured by heat or light. After the holes are filled, the stencil isremoved from the substrate and the stenciling composition is cured to asolid state.

Like the syringe method above, using the stencil method can be difficultto control the geometry and layer thickness of the phosphor containingpolymer. The stenciling composition may not fully fill the stencilopening such that the resulting layer is not uniform. The phosphorcontaining composition can also stick to the stencil opening whichreduces the amount of composition remaining on the LED. The stencilopenings may also be misaligned to the LED. These problems can result inLEDs having non-uniform color temperature and LEDs that are difficult toconsistently reproduce with the same or similar emissioncharacteristics.

Various coating processes of LEDs have been considered, including spincoating, spray coating, electrostatic deposition (ESD), andelectrophoretic deposition (EPD). Processes such as spin coating orspray coating typically utilize a binder material during the phosphordeposition, while other processes require the addition of a binderimmediately following their deposition to stabilize the phosphorparticles/powder.

With these approaches the key challenge is accessing the wire bond padon the device after the coating process. Accessing the wire bond bystandard wafer fabrication techniques is difficult with typical siliconebinding material, as well as other binder materials such as epoxies orglass. Silicones are not compatible with commonly used wafer fabricationmaterials such as acetone, as well as some developers, and resiststrippers. This can limit the options and choices for the particularsilicones and process steps. Silicones are also cured at hightemperature (greater than 150° C.), which is beyond the glass transitiontemperature of commonly used photoresists. Cured silicone films withphosphor are also difficult to etch and have a very slow etch rate inchlorine and CF₄ plasma, and wet etching of cured silicones is typicallyinefficient.

SUMMARY OF THE INVENTION

The present invention discloses new methods for fabricatingsemiconductor devices such as LED chips at the wafer level, anddiscloses LED chips and LED chip wafers fabricated using the methods.One method for fabricating light emitting diode (LED) chips according tothe present invention comprises providing a plurality of LEDs typicallyon a substrate. Pedestals are formed on the LEDs with each of thepedestals in electrical contact with one of the LEDs. A coating isformed over said LEDs, with the coating burying at least some of thepedestals. The coating is then planarized leaving some of said coatingmaterial on said LEDs while exposing at least some of the buriedpedestals, making them available for contacting. The present inventiondiscloses similar methods used for fabricating LED chips comprising LEDsflip chip mounted on a carrier substrate. Similar methods according tothe present invention can also be used for fabricating othersemiconductor devices.

One embodiment of a light emitting diode (LED) chip wafer fabricatedusing methods according to the present invention comprises a pluralityof LEDs on a substrate wafer and a plurality of pedestals, each of whichis in electrical contact with one of the LEDs. A coating at leastpartially covers the LEDs with at least some of the pedestals extendingthrough and to the surface of the coating. The pedestals are exposed atthe surface of the coating.

One embodiment of a light emitting diode (LED) chip manufactured usingmethods according to the present invention comprises an LED on asubstrate and a pedestal in electrical contact with the LED. A coatingat least partially covering the LED, with the pedestal extending throughand to the surface of the coating and exposed at the surface of thecoating.

In accordance with certain aspects of the present invention, the coatingcan include phosphor particles that downconvert at least some of thelight emitted from the active region of the LED chip to produce whitelight, thereby producing a white LED chip.

These and other aspects and advantages of the invention will becomeapparent from the following detailed description and the accompanyingdrawings which illustrate by way of example the features of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a through 1 e are sectional views of one embodiment of an LEDchip wafer at fabrication steps in one method according to the presentinvention;

FIG. 2 is a sectional view of another embodiment of an LED chip waferaccording to the present invention having a reflective layer;

FIGS. 3 a through 3 e are sectional views of one embodiment of anflip-wafer bonded LED chip wafer at fabrication steps in another methodaccording to the present invention;

FIG. 4 is a sectional view of another embodiment of an LED chip waferaccording to the present invention having a reflective layer;

FIGS. 5 a through 5 d are sectional views of another embodiment of anLED chip wafer at fabrication steps in a method according to the presentinvention utilizing a prefabricated coating;

FIGS. 6 a through 6 c are sectional views of another embodiment of anLED chip wafer at fabrication steps in a method according to the presentinvention having recesses in the coating;

FIG. 7 is a sectional view of another embodiment of an LED chip waferaccording to the present invention;

FIG. 8 is also a sectional view of another embodiment of an LED chipwafer according to the present invention;

FIG. 9 is a sectional view of one embodiment of an LED array accordingto the present invention;

FIG. 10 is a sectional view of another embodiment of an LED arrayaccording to the present invention;

FIG. 11 is a sectional view of an embodiment of an LED chip waferaccording to the present invention having a transparent substrate;

FIG. 12 is a sectional view of another embodiment of an LED chip waferaccording to the present invention having a transparent substrate;

FIG. 13 is a sectional view of another embodiment of an flip-chip LEDchip wafer according to the present invention;

FIG. 14 is a sectional view of another embodiment of an LED chip havinga phosphor loading carrier substrate;

FIGS. 15 a through 15 d are sectional views of another embodiment of anLED chip wafer at fabrication steps in a method according to the presentinvention utilizing a trenched substrate.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides fabrication methods that are particularlyapplicable to wafer level coating of semiconductor devices such as LEDs.The present invention also provides semiconductor devices, such as LEDsfabricated using these methods. The present invention allows coating ofLEDs at the wafer level with a down-converter layer (e.g. phosphorloaded silicone) while still allowing access to one or more of thecontacts for wire bonding. According to one aspect of the presentinvention, electrically conducting pedestals/posts are formed on one orboth of the LED contacts (bond pads) while the LEDs are at the waferlevel. These pedestals can be fabricated using known techniques such aselectroplating, electroless plating, stud bumping, or vacuum deposition.The wafer can then be blanket coated with a down-converter coatinglayer, burying the LEDs, contacts and pedestals. Each of the pedestalsact as a vertical extension of its contact, and although the blanketcoating with the down-converter coating temporarily covers thepedestals, the coating can be planarized and thinned to expose the topsurface or top portion of the pedestals. The pedestals should be tallenough (10-100 μm) to project through the desired final coatingthickness. After planarizing the pedestals are exposed for externalconnection such as by wire bonding. This process occurs at the waferlevel and as a subsequent fabrication step, the individual LEDs chipscan be separated/singulated from the wafer using known processes.

The present invention eliminates complex wafer fabrication processes toaccess wire bond pads after blanket coating. Instead a simple and costeffective approach is utilized. It allows for wafer level coating ofsemiconductor devices without the need for alignment. A wide variety ofcoating technologies can be used such as spin-coating of phosphor loadedsilicone mixture, or electrophoretic deposition of phosphor followed byblanket coating of silicone or other binding material. Mechanicalplanarization allows thickness uniformity over the wafer and thicknessuniformity of the coat can be achieved over a wide thickness range (e.g.1 to 100 μm). White LED chip color point may be fine tuned bycontrolling the final coat thickness, including using an iterativeapproach (e.g. grind, test, grind, etc.) which will result in tightlybinned white LEDs. This approach is also scalable to large wafer sizes.

The present invention is described herein with reference to certainembodiments but it is understood that the invention can be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. In particular, the present invention isdescribed below in regards to coating LEDs with a down-converter coatingthat typically comprises a phosphor loaded binder (“phosphor/bindercoating”), but it is understood that the present invention can be usedto coat LEDs with other materials for down-conversion, protection, lightextraction or scattering. It is also understood that the phosphor bindercan have scattering or light extraction particles or materials, and thatthe coating can be electrically active. The methods according to thepresent invention can also be used for coating other semiconductordevices with different materials. Additionally, single or multiplecoatings and/or layers can be formed on the LEDs. A coating can includeno phosphors, one or more phosphors, scattering particles and/or othermaterials. A coating may also comprise a material such as an organic dyethe provides down-conversion. With multiple coatings and/or layers, eachone can include different phosphors, different scattering particles,different optical properties, such as transparency, index of refraction,and/or different physical properties, as compared to other layers and/orcoatings.

It is also understood that when an element such as a layer, region orsubstrate is referred to as being “on” another element, it can bedirectly on the other element or intervening elements may also bepresent. Furthermore, relative terms such as “inner”, “outer”, “upper”,“above”, “lower”, “beneath”, and “below”, and similar terms, may be usedherein to describe a relationship of one layer or another region. It isunderstood that these terms are intended to encompass differentorientations of the device in addition to the orientation depicted inthe figures.

Although the terms first, second, etc. may be used herein to describevarious elements, components, regions, layers and/or sections, theseelements, components, regions, layers and/or sections should not belimited by these terms. These terms are only used to distinguish oneelement, component, region, layer or section from another region, layeror section. Thus, a first element, component, region, layer or sectiondiscussed below could be termed a second element, component, region,layer or section without departing from the teachings of the presentinvention.

Embodiments of the invention are described herein with reference tocross-sectional view illustrations that are schematic illustrations ofidealized embodiments of the invention. As such, variations from theshapes of the illustrations as a result, for example, of manufacturingtechniques and/or tolerances are expected. Embodiments of the inventionshould not be construed as limited to the particular shapes of theregions illustrated herein but are to include deviations in shapes thatresult, for example, from manufacturing. A region illustrated ordescribed as square or rectangular will typically have rounded or curvedfeatures due to normal manufacturing tolerances. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region of a device andare not intended to limit the scope of the invention.

FIGS. 1 a through 1 e show one embodiment of wafer level LED chips 10manufactured using a method according to the present invention.Referring now to FIG. 1 a, the LEDs chips 10 are shown at a wafer levelof their fabrication process. That is, the LEDs chips 10 have not beenthrough all the steps necessary before being separated/singulated fromwafer into individual LED chips. Phantom lines are included to showseparation or dicing line between the LED chips 10 and followingadditional fabrication steps, and as shown in FIG. 1 e the LEDs chipscan be separated into individual devices. FIGS. 1 a through 1 e alsoshow only two devices at the wafer level, but it is understood that manymore LED chips can be formed from a single wafer. For example, whenfabricating LED chips having a 1 millimeter (mm) square size, up to 4500LED chips can be fabricated on a 3 inch wafer.

Each of the LED chips 10 comprises a semiconductor LED 12 that can havemany different semiconductor layers arranged in different ways. Thefabrication and operation of LEDs is generally known in the art and onlybriefly discussed herein. The layers of the LED 10 can be fabricatedusing known processes with a suitable process being fabrication usingmetal organic chemical vapor deposition (MOCVD). The layers of the LEDs12 generally comprise an active layer/region 14 sandwiched between firstand second oppositely doped epitaxial layers 16, 18, all of which areformed successively on a substrate 20. In this embodiment the LEDs 12are shown as separate devices on the substrate 20. This separation canbe achieved by having portions of the active region 14 and doped layers16, 18 etched down to the substrate 20 to form the open areas betweenthe LEDs 12. In other embodiments and as described in more detail below,the active layer 14 and doped layers 16, 18 can remain continuous layerson the substrate 20 and can be separated into individual devices whenthe LED chips are singulated.

It is understood that additional layers and elements can also beincluded in the LED 12, including but not limited to buffer, nucleation,contact and current spreading layers as well as light extraction layersand elements. The active region 14 can comprise single quantum well(SQW), multiple quantum well (MQW), double heterostructure or superlattice structures. In one embodiment, the first epitaxial layer 16 isan n-type doped layer and the second epitaxial layer 18 is a p-typedoped layer, although in other embodiments the first layer 16 can bep-type doped and the second layer 18 n-type doped. The first and secondepitaxial layers 16, 18 are hereinafter referred to as n-type and p-typelayers, respectively.

The region 14 and layers 16, 18 of the LEDs 12 may be fabricated fromdifferent material systems, with preferred material systems beingGroup-III nitride based material systems. Group-III nitrides refer tothose semiconductor compounds formed between nitrogen and the elementsin the Group III of the periodic table, usually aluminum (Al), gallium(Ga), and indium (In). The term also refers to ternary and quaternarycompounds such as aluminum gallium nitride (AlGaN) and aluminum indiumgallium nitride (AlInGaN). In a preferred embodiment, the n- and p-typelayers 16, 18 are gallium nitride (GaN) and the active region 14 isInGaN. In alternative embodiments the n- and p-type layers 16, 18 may beAlGaN, aluminum gallium arsenide (AlGaAs) or aluminum gallium indiumarsenide phosphide (AlGaInAsP).

The substrate 20 can be made of many materials such at sapphire, siliconcarbide, aluminum nitride (AlN), GaN, with a suitable substrate being a4H polytype of silicon carbide, although other silicon carbide polytypescan also be used including 3C, 6H and 15R polytypes. Silicon carbide hascertain advantages, such as a closer crystal lattice match to Group IIInitrides than sapphire and results in Group III nitride films of higherquality. Silicon carbide also has a very high thermal conductivity sothat the total output power of Group-III nitride devices on siliconcarbide is not limited by the thermal dissipation of the substrate (asmay be the case with some devices formed on sapphire). SiC substratesare available from Cree Research, Inc., of Durham, N.C. and methods forproducing them are set forth in the scientific literature as well as ina U.S. Pat. Nos. Re. 34,861; 4,946,547; and 5,200,022. In the embodimentshown, the substrate 20 is at the wafer level, with the plurality ofLEDs 12 formed on the wafer substrate 20.

Each of the LEDs 12 can have first and second contacts 22, 24. In theembodiment shown, the LEDs have a vertical geometry with the firstcontact 22 on the substrate 20 and the second contact 24 on the p-typelayer 18. The first contact 22 is shown as one layer on the substrate,but when the LED chips are singulated from the wafer the first contact22 will also be separated such that each LED chip 10 has its own portionof the first contact 22. An electrical signal applied to the firstcontact 22 spreads into the n-type layer 16 and a signal applied to thesecond contact 24 spreads into the p-type layer 18. In the case ofGroup-III nitride devices, it is well known that a thin semitransparentcurrent spreading layer typically covers some or all of the p-type layer18. It is understood that the second contact 24 can include such a layerwhich is typically a metal such as platinum (Pt) or a transparentconductive oxide such as indium tin oxide (ITO). The first and secondcontacts 22, 24 are hereinafter referred to as the n-type and p-typecontacts respectively.

The present invention can also be used with LEDs having lateral geometrywherein both contacts are on the top of the LEDs. A portion of thep-type layer 18 and active region is removed, such as by etching toexpose a contact mesa on the n-type layer 16. The boundary of theremoved portion of the of the active region 14 and p-type layer 18 isdesignated by vertical phantom line 25. A second lateral n-type contact26 (also shown in phantom) is provided on the mesa of the n-type layer16. The contacts can comprise known materials deposited using knowndeposition techniques.

Referring now to FIG. 1 b, and according to the present invention, ap-type contact pedestal 28 is formed on the p-type contact 24 that isutilized to make electrical contact to the p-type contact 24 aftercoating of the LEDs 12. The pedestal 28 can be formed of many differentelectrically conductive materials and can be formed using many differentknown physical or chemical deposition processes such as electroplating,electroless plating, or stud bumping, with the preferred contactpedestal being gold (Au) and formed using stud bumping. This method istypically the easiest and most cost effective approach. The pedestal 28can be made of other conductive materials beyond Au, such as copper (Cu)or nickel (Ni) or Indium, or combinations thereof.

The process of forming stud bumps is generally known and only discussedbriefly herein. Stud bumps are placed on the contacts (bond pads)through a modification of the “ball bonding” process used inconventional wire bonding. In ball bonding, the tip of the bond wire ismelted to form a sphere. The wire bonding tool presses this sphereagainst the contact, applying mechanical force, heat, and/or ultrasonicenergy to create a metallic connection. The wire bonding tool nextextends the gold wire to the connection pad on the board, substrate, orlead frame, and makes a “stitch” bond to that pad, and finishes bybreaking off the bond wire to begin another cycle. For stud bumping, thefirst ball bond is made as described, but the wire is then broken closeabove the ball. The resulting gold ball, or “stud bump” remains on thecontact and provides a permanent, reliable connection through to theunderlying contact metal. The stud bumps can then be flattened (or“coined”) by mechanical pressure to provide a flatter top surface andmore uniform bump heights, while at the same time pressing any remainingwire into the ball.

The height of the pedestal 28 can vary depending on the desiredthickness of the phosphor loaded binder coating and should be highenough to match or extend above the top surface of the phosphor loadedbinder coating from the LED. The height can exceed 200 μm, with typicalpedestal height in the range of 20 to 60 μm. In some embodiments, morethan one stud bump can be stacked to achieve the desired pedestalheight. The stud bumps or other forms of the pedestal 28 can also have areflecting layer or can be made of a reflective material to minimizeoptical losses.

For the vertical geometry type LEDs 12 shown, only one pedestal 28 isneeded for the p-type contact 24. For alternative lateral geometry LEDsa second n-type pedestal 30 (shown in phantom) is formed on the lateralgeometry n-type contact 26, typically of the same materials, tosubstantially the same height as the p-type pedestal 28, and formedusing the same processes.

Referring now to FIG. 1 c, the wafer is blanketed by a phosphor/bindercoating 32 that covers each of the LEDs 12, and its contact 22, and hasa thickness such that it covers/buries the pedestal 28. For lateralgeometry devices, the contact 26 and pedestal 30 are also buried. Thepresent invention provides the advantage of depositing the phosphorcoating over the LEDs 12 at the wafer level without the need foralignment over particular devices or features. Instead, the entire waferis covered, which provides for a simpler and more cost effectivefabrication process. The phosphor coating can be applied using differentprocesses such as spin coating, electrophoretic deposition,electrostatic deposition, printing, jet printing or screen printing.

In a preferred embodiment, the phosphor can be deposited over the waferin a phosphor/binder mixture using spin coating. Spin coating isgenerally known in the art and generally comprises depositing thedesired amount of binder and phosphor mixture at the center of thesubstrate and spinning the substrate at high speed. The centrifugalacceleration causes the mixture to spread to and eventually off the edgeof the substrate. Final layer thickness and other properties depend onthe nature of the mixture (viscosity, drying rate, percent phosphor,surface tension, etc.) and the parameters chosen for the spin process.For large wafers it may be useful to dispense the phosphor/bindermixture over the substrate before spinning the substrate at high speed.

In another embodiment, the phosphor is deposited on the wafer usingknown electrophoretic deposition methods. The wafer and its LEDs areexposed to a solution containing phosphor particles suspended in aliquid. An electrical signal is applied between the solution and theLEDs which creates an electrical field that causes the phosphorparticles to migrate to and deposit on the LEDs. The process typicallyleaves the phosphor blanketed over the LEDs in powder form. A binder canthen be deposited over the phosphor with the phosphor particles sinkinginto the binder to form the coating 32. The binder coating can beapplied using many known methods and in one embodiment, the bindercoating can be applied using spin coating.

The phosphor/binder coating 32 can then be cured using many differentcuring methods depending on different factors such as the type of binderused. Different curing methods include but are not limited to heat,ultraviolet (UV), infrared (IR) or air curing.

Different factors determine the amount of LED light that will beabsorbed by the phosphor/binder coating in the final LED chips,including but not limited to the size of the phosphor particles, thepercentage of phosphor loading, the type of binder material, theefficiency of the match between the type of phosphor and wavelength ofemitted light, and the thickness of the phosphor/binding layer. Thesedifferent factors can be controlled to control the emission wavelengthof the LED chips according to the present invention.

Different materials can be used for the binder, with materialspreferably being robust after curing and substantially transparent inthe visible wavelength spectrum. Suitable material include silicones,epoxies, glass, spin-on glass, BCB, polymides and polymers, with thepreferred material being silicone because of its high transparency andreliability in high power LEDs. Suitable phenyl- and methyl-basedsilicones are commercially available from Dow® Chemical. In otherembodiments, the binder material can be engineered to be index matchedwith the features such as the chip (semiconductor material) and growthsubstrate, which can reduce total internal reflection (TIR) and improvelight extraction.

Many different phosphors can be used in the coating 32 according to thepresent invention. The present invention is particularly adapted to LEDchips emitting white light. In one embodiment according to the presentinvention LEDs 12 emit light in the blue wavelength spectrum and thephosphor absorbs some of the blue light and re-emits yellow. The LEDchips 10 emit a white light combination of blue and yellow light. In oneembodiment the phosphor comprises commercially available YAG:Ce,although a full range of broad yellow spectral emission is possibleusing conversion particles made of phosphors based on the(Gd,Y)₃(Al,Ga)₅O₁₂:Ce system, such as the Y₃Al₅O₁₂:Ce (YAG). Otheryellow phosphors that can be used for white emitting LED chips include:Tb_(3-x)RE_(x)O₁₂:Ce(TAG); RE=Y, Gd, La, Lu; orSr_(2-x-y)Ba_(x)Ca_(y)SiO₄:Eu.

First and second phosphors can also be combined for higher CRI white ofdifferent white hue (warm white) with the yellow phosphors abovecombined with red phosphors. Different red phosphors can be usedincluding:

Sr_(x)Ca_(1-x)S:Eu, Y; Y=halide;

CaSiAlN₃:Eu; or

Sr_(2-y)Ca_(y)SiO₄:Eu

Other phosphors can be used to create saturated color emission byconverting substantially all light to a particular color. For example,the following phosphors can be used to generate green saturated light:

SrGa₂S₄:Eu;

Sr_(2-y)Ba_(y)SiO₄:Eu; or

SrSi₂O₂N₂:Eu.

The following lists some additional suitable phosphors used asconversion particles in an LED chips 10, although others can be used.Each exhibits excitation in the blue and/or UV emission spectrum,provides a desirable peak emission, has efficient light conversion, andhas acceptable Stokes shift:

Yellow/Green

(Sr,Ca,Ba)(Al,Ga)₂S₄:Eu²⁺

Ba₂(Mg,Zn)Si₂O₇:Eu²⁺

Gd_(0.46)Sr_(0.31)Al_(1.23)O_(x)F_(1.38):Eu²⁺ _(0.06)

(Ba_(1-x-y)Sr_(x)Ca_(y))SiO₄:Eu

Ba₂SiO₄:Eu²⁺

Red

Lu₂O₃:Eu³⁺

(Sr_(2-x)La_(x))(Ce_(1-x)Eu_(x))O₄

Sr₂Ce_(1-x)Eu_(x)O₄

Sr_(2-x)Eu_(x)CeO₄

SrTiO₃:Pr³⁺,Ga³⁺

CaAlSiN₃:Eu²⁺

Sr₂Si₅N₈:Eu²⁺

Different sized phosphor particles can be used including but not limitedto 10-100 nanometer (nm)-sized particles to 20-30 μm sized particles, orlarger. Smaller particle sizes typically scatter and mix colors betterthan larger sized particles to provide a more uniform light. Largerparticles are typically more efficient at converting light compared tosmaller particles, but emit a less uniform light. In one embodiment, theparticle sizes are in the range of 2-5 μm. In other embodiments, thecoating 32 can comprise different types of phosphors or can comprisemultiple phosphor coatings for monochromatic or polychromatic lightsources.

The coating 32 can also have different concentrations or loading ofphosphor materials in the binder, with a typical concentration being inrange of 30-70% by weight. In one embodiment, the phosphor concentrationis approximately 65% by weight, and is preferably uniformly dispersedthroughout the binder. Still in other embodiments the coating cancomprise multiple layers of different concentrations of types ofphosphors, or a first coat of clear silicone can be deposited followedby phosphor loaded layers.

As discussed above, the pedestal 28 (and pedestal 30 for lateraldevices) are buried by the coating 32, which allows for the LED chips 10to be coated without the need for alignment. After the initial coatingof the LED chips, further processing is needed to expose the pedestal28. Referring now the FIG. 1 d, the coating 32 is thinned or planarizedso that the pedestals 28 are exposed through the coating's top surface.Many different thinning processes can be used including known mechanicalprocesses such as grinding, lapping or polishing, preferably after thebinder has cured. Other fabrication methods can comprise a squeegee tothin the coating before cured or pressure planarization can also be usedbefore the coating is cured. Still in other embodiments the coating canbe thinned using physical or chemical etching, or ablation. The thinningprocess not only exposes the pedestals, but also allows for planarizingof the coating and for control of the final thickness of the coating.

Following planarization, the surface root mean squared roughness of thecoating should be approximately 10 nm or less, although the surface canhave other surface roughness measurements. In some embodiments thesurface can be textured during planarization. In other embodiments,after planarization the coating or other surfaces, can be textured suchas by laser texturing, mechanical shaping, etching (chemical or plasma),or other processes, to enhance light extraction. Texturing results insurface features that are 0.1-5 μm tall or deep, and preferably 0.2-1μm. In other embodiments, the surface of the LEDs 12 can also betextured or shaped for improved light extraction.

Referring now to FIG. 1 e, the individual LED chips 10 can be singulatedfrom the wafer using known methods such as dicing, scribe and breaking,or etching. The singulating process separates each of the LED chips 10with each having substantially the same thickness of coating 32, and asa result, substantially the same amount of phosphor and emissioncharacteristics. This allows for reliable and consistent fabrication ofLED chips 10 having similar emission characteristics. Followingsingulating the LED chips can be mounted in a package, or to a submountor printed circuit board (PCB) without the need for further processingto add phosphor. In one embodiment the package/submount/PCB can haveconventional package leads with the pedestals electrically connected tothe leads. A conventional encapsulation can then surround the LED chipand electrical connections. In another embodiment, the LED chip can beenclosed by a hermetically sealed cover with an inert atmospheresurrounding the LED chip at or below atmospheric pressure.

For the LED chips 10, light from the LED 12 that is emitted towardsubstrate 20 can pass out of the LED chip 10 through the substratewithout passing through the phosphor/binder coating 32. This can beacceptable for generating certain colors or hues of light. Inembodiments where this substrate emission is to be prevented orminimized, the substrate 20 can be opaque so that light from the LED 12emitted toward the substrate 20 is blocked or absorbed so that mostlight emitting from the LED chip 10 comes from light passing through thecoating 32.

FIG. 2 shows anther embodiment of a LED chips 40 that are similar to theLED chips 10 described above and shown in FIGS. 1 a through 1 e, buthaving additional features to encourage emission of LED chip lighttoward the top of the LED chips 40 and minimize light passing into thesubstrate 20. For similar features as those in LED chips 10, the samereference numbers will be used herein. Each of the LED chips 40comprises LEDs 12 formed on a substrate 20 and having n-type layer 16,active region 14 and p-type layer 18 formed successively on thesubstrate 20. LED chips 40 further comprise n-type contact 22, p-typecontact 24, p-type pedestal 28 and coating 32. The coating 32 isplanarized to expose the pedestal 28. The LED chips 40 can alternativelyhave lateral geometry with the additional pedestal 30

LED chips 40 also comprise a reflective layer 42 that is arranged toreflect light emitted from the active region toward the substrate 20,back toward the top of the LED chips 40. This reflective layer 42reduces the emission of light from the LEDs 12 that does not passthrough conversion material before emitting from the LED chips 40, suchas through the substrate 20 and encourages emission toward the top ofthe LED chips 40 and through the coating 32.

The reflective layer 42 can be arranged in different ways and indifferent locations in the LED chip 40, with the layer 42 as shownarranged between the n-type layer 16 and the substrate 20. The layer canalso extend on the substrate 20 beyond the vertical edge of the LEDchips 12. In other embodiments the reflective layer is only between then-type layer 16 and the substrate. The layer 42 can comprise differentmaterials including but not limited to a metal or a semiconductorreflector such as a distributed Bragg reflector (DBR).

As mentioned above, in some embodiments the active region 14 and the n-and p-type layers 16, 18 can be continuous layers on the substrate 20 asshown by phantom lines between the LEDs 12. In these embodiments, theLEDs are not separated until the step when the LED chips 40 aresingulated. Accordingly, the resulting LED chips may have a layer of thecoating 32 over the top surface of the LEDs. This can allow for emissionof the active region light out the side surfaces of the LEDs 12, but inembodiments utilizing this LEDs in relation to the surrounding features,this emission of light without encountering phosphor material can beminimal compared to the amount of light passing through the phosphormaterial.

The methods according to the present invention can be used to coat manydifferent devices and LEDs. FIGS. 3 a through 3 e show a different LEDchip 60 having a structure different from the LED chip 10 describedabove and shown in FIGS. 1 a through 1 e. Referring first to FIG. 3 a,the LED chip 60 is also at wafer level and shown prior to singulating.It comprises LEDs 62 that are not on a growth substrate, but are insteadflip-wafer bonded to a carrier substrate 64. In this embodiment, thegrowth substrate can comprise the materials described above for growthsubstrate 20 in FIGS. 1 a through 1 e, but in this embodiment the growthsubstrate is removed after (or before) flip-wafer bonding, with thesubstrate removed using known grinding and/or etching processes. TheLEDs 62 are mounted to the carrier substrate 64 by layer 66, which istypically one or more bond/metal layers, and which also serve to reflectlight incident on it. In other embodiments, the growth substrate or atleast portions thereof remain. The growth substrate or the remainingportions can be shaped or textured to enhance light extraction from theLEDs 62.

Many different material systems can be used for the LEDs, with apreferred material system being the Group-III nitride material systemgrown using known processes as described above. Like the LEDs 12 inFIGS. 1 a-1 e, each of the LEDs 62 generally comprises an active region68 sandwiched between n-type and p-type epitaxial layers 70, 72 althoughother layers can also be included. Because LEDs 62 are flip-waferbonded, the top layer is the n-type layer 70, while the p-type layer 72is the bottom layer arranged between the active region 68 and thebond/metal layer 66. The carrier substrate can be many different knownmaterials, with a suitable material being silicon.

For vertical geometry LED chips 60, an n-type contact 74 can be includedon top surface of each of the LEDs, and a p-type contact 76 can beformed on the carrier substrate 64. The n- and p-type contacts 74, 76can also be made of conventional conductive materials deposited usingknown techniques similar to the first and second contacts 22, 24 shownin FIGS. 1 a through 1 e and described above. As also described above,the LEDs can have a lateral geometry with the n- and p-type contacts onthe top of the LEDs.

Referring now to FIG. 3 b, each of the LED chips 60 can have a pedestal78 formed on its first contact 70, with each pedestal being formed ofthe same material and using the same methods as those described abovefor pedestal 28 in FIGS. 1 b through 1 e. As shown in FIG. 3 c the LEDchip wafer can then be covered by a blanket coating 80 preferablycomprising a phosphor loaded binder. The same phosphors and binder canbe used as those for the coating 32 described above and shown in FIGS. 1c through 1 e, and can be deposited using the same methods. The coating80 covers and buries the LEDs 62, their first contacts 74 and thepedestals 78, with the coating 80 being deposited without alignmentsteps.

Referring now to FIG. 3 d, the coating 80 can be planarized or thinnedto expose the pedestals 78 and to control thickness of the coating 80using the methods described above. Referring now to FIG. 3 e, theindividual LED chips 60 can be singulated from the wafer using themethods described above. These devices can then be packaged or mountedto a submount or PCB. In other embodiments the carrier substrate can beremoved, leaving a coated LED that can then be packaged or mounted to asubmount or PCB.

The flip-wafer bonded LEDs can also have reflective elements or layersto encourage light emission in the desired direction. FIG. 4 shows LEDchips 90 at the wafer level that are similar to the LED chips 60 shownin FIGS. 3 a through 3 e and described above. For similar features thesame reference numbers are used herein, and although LED chips 90 areshown having vertical geometry LEDs 62, it is understood that lateralgeometry LEDs can also be used. The LED chips 90 comprise LEDs 62mounted to a substrate 64 that can either be a carrier or growthsubstrate. Each of the LEDs 62 comprises an active layer 68, n-typelayer 70, p-type layer 72, p-type contact 76, n-type contact 74, andpedestal 78 as described above, and a phosphor loaded binder coating 80is formed over the LEDs also as described above. In this embodiment,however, a reflective layer 92 is included between the LEDs 62 and thesubstrate 64 that can comprise a highly reflective metal or reflectivesemiconductor structures such as a DBR. The reflective layer 92 reflectsLED light that is emitted toward the substrate 64 and helps preventlight from passing into the substrate where at least some of the lightcan be absorbed by the substrate 64. This also encourages light emissionfrom the LED chips 90 toward the top of the LED chips 90. It isunderstood that a bond/metal layer (not shown) can also be includedbelow the reflective layer or in other locations, particularly in theembodiments where the substrate 64 is a carrier substrate. The LED chips90 can also comprise a p-contact layer adjacent to the p-type layer 72to encourage ohmic contact to the layers below.

FIGS. 5 a through 5 d show another embodiment of LED chips 100fabricated according to the present invention that are similar to theLED chips 60 described above and shown in FIGS. 3 a through 3 e. It isunderstood, however, that this method can also be used with nonflip-wafer bonded embodiments such as the embodiment described above andshown in FIGS. 1 a through 1 e. Referring first to FIG. 5 a, the LEDchips 100 comprise vertical LEDs 62 mounted to a substrate 64 that inthis case is a carrier substrate. It is understood that lateral LEDs canalso be used as described above. Each of the LEDs 62 comprises activelayer 68, n-type layer 70, p-type layer 72, p-type contact 76, n-typecontact 74, and pedestal 78 as described above. For LED chips 100,however, are covered by a prefabricated coating layer 102 that can havethe phosphor (and other) materials described above fixed in a binderalso made of the materials described above.

Referring now to FIG. 5 b, the layer 102 is placed over and covering theLEDs 62 and their pedestals 78 to provide a conformal coating. In oneembodiment a bonding material can be included between the layer 102 andthe LED chips 100 for adhesion, with typical adhesives being used suchas silicones or epoxies. To further encourage conformal coating, thelayer 102 can be heated or a vacuum can be applied to pull the layer 102down over the LED chips 100. The layer 102 can also be provided in astate where the binder is not fully cured so that the layer 102 morereadily conforms to the LED chips. Following conformal placement of thelayer 102, the binder can be exposed to its final curing.

Referring now to FIG. 5 c, the layer 102 can be planarized using themethods described above to expose the pedestals 78, making themavailable for contacting. As shown in FIG. 5 d, the LED chips 100 canthen be singulated using the methods described above.

The fabrication method for LED chips 100 allows for the thickness of thephosphor/binder to be accurately controlled by controlling the thicknessof the layer 102. This method also allows for the use of different layerthicknesses and composition for different desired emissioncharacteristics for the LED chips 100.

FIGS. 6 a through 6 c show still another embodiment of LED chips 110according to the present invention similar to LED chips 60. Referringfirst to FIG. 6 a, each of the LED chips 110 has vertical LEDs 62mounted to a substrate 64 that can either be a carrier or growthsubstrate. Each of the LEDs 62 comprises active layer 68, n-type layer70, p-type layer 72, p-type contact 76, n-type contact 74, and pedestal78 as described above. A coating 112 made of the materials describedabove is included over the LEDs 62, burying the pedestals 78.

Referring to FIG. 6 b, in this embodiment the coating 112 is notplanarized to expose the pedestals 78. Instead, the coating remains at alevel higher than the pedestals and a portion of the coating 112 buryingthe pedestal 78 is removed leaving recessed portions 114 in the coating112. The pedestals 78 are exposed through the recessed portions 114 forcontacting. Many different methods can be used to remove the coatingsuch as conventional patterning or etching processes. Referring now toFIG. 6 c, the LED chips 110 can then be singulated using the methodsdescribed above.

This method of forming recessed portions 114 can be used in conjunctionwith planarizing of the coating 112. The layer 112 can be planarized tothe level that provides the desired emission characteristics of the LEDchip 110, which may be above the pedestals 78. The recessed portions 114can then be formed to access the pedestals. This allows for formingpedestals of reduced height lower than the coating, which can reducefabrication costs related to forming the pedestals 78. This process canrequire some alignment with forming the recessed portions, but thecoating 112 is still applied without the need for alignment.

The pedestals in the LED chips embodiments above are described ascomprising a conductive material such as Au, Cu, Ni or In, preferablyformed using stud bumping processes. Alternatively, the pedestals can bemade of different materials and can be formed using different methods.FIG. 7 shows another embodiment of LED chips 120 comprising LEDs 122flip-wafer bonded on a carrier substrate 124. In this embodiment, thepedestal 136 comprises a semiconductor material 138 formed generally inthe shape of a pedestal 136. The semiconductor material 138 can be onthe first contact, or as shown can be on the first epitixial layer 130.A pedestal layer 140 of conductive material is included on the topsurface of the semiconductor material 138 and extending to the topsurface of the first epitaxial layer 130 and forming an n-type contact.

The semiconductor material 138 can be formed in many different ways andcan comprise many different materials, such as the material comprisingthe LED epitaxial layers or the growth substrate material, e.g. GaN,SiC, sapphire, Si, etc. In one embodiment, the semiconductor material138 can be etched from the epitaxial layers, and then coated with thepedestal layer 140. In other embodiments, portions of the growthsubstrate can remain on the epitaxial layers during removal of thegrowth substrate from the LEDs 122. The remaining growth substrateportions can then be covered by the pedestal layer 140.

FIG. 8 shows another embodiment of LED chips 150 still in wafer formthat are similar to the LED chips 120 in FIG. 7, and the same referencenumbers are used for similar features herein. The LED chips 150 compriseLEDs 122 flip-wafer bonded on a carrier substrate 124 by bond/metallayer 126. A pedestal 154 is formed on each of the LEDs 122, preferablyon the n-type contact 155. The pedestal 154 comprises a patternablematerial 156 in substantially the shape of the pedestal 154 that iscovered with a pedestal layer 158 of conductive material that extends tothe first contact 152. The patternable material 156 can comprisedifferent materials compatible with LED fabrication and operation suchas BCB, polymides and dielectrics. These materials can be formed on theLEDs 112 using known processes. Alternatively, pedestal 154 can beformed using patternable and electrically conducting materials such assilver epoxy or printable inks, in which case layer 158 may not berequired. Other methods and approaches for fabricating pedestals can beused, some of which are described in John Lau, “Flip-Chip Technologies”,McGraw Hill, 1996.

Like the embodiments above, the wafer comprising the LED chips 120 and150 can be blanketed by a layer of coating material, burying the LEDchips and their pedestals. The coating material can comprise thephosphors and binders described above, and can be thinned using themethods described above to expose the pedestals through the coatingmaterials. The LED chips can then be singulated using the methodsdescribed above.

The present invention can also be used to fabricate wafer level emitterarrays. FIG. 9 shows one embodiment of wafer level LED array 170 thatcomprises LEDs 172 flip-wafer bonded on a carrier substrate 174 by abond/metal layer 176. The LEDs comprise an active region 178 betweenfirst and second epitaxial layers 180, 182 with a first contact 184 onthe first epitaxial layer 180. A pedestal 186 is included on the firstcontact 184 and a coating 188 of phosphor loaded binder coating blanketsthe LEDs 172, contacts 184 and pedestals 186, with the coating beingthinned to expose the top of the pedestals 186. For the LED array 170however, the individual LED chips are not singulated. Instead, aninterconnecting metal pad 190 is included on the surface of the LED 172,interconnecting the exposed tops of the pedestals 186 in a parallelfashion. An electrical signal applied to the metal pad 190 conducts tothe LEDs having their pedestals 186 coupled to the metal pad 190,illuminating the LEDs in an array. It is understood that the LED arraycan comprise many different numbers of LEDs arranged in different ways,such as in a row or block, depending on the LEDs that are interconnectedby the metal pad 190.

FIG. 10 shows another embodiment of an LED array 200 according to thepresent invention also having LEDs 202 flip-wafer bonded to a carriersubstrate 204, with each of the LEDs 202 comprising an active region 208between first and second epitaxial layers 210, 212. A first contact 214is on the first epitixial layer 210 with a pedestal 216 formed on thefirst contact 214. A phosphor loaded binder coating 218 is included overthe LEDs 202, first contacts 214 and pedestals 216, with the top surfaceof the pedestals 216 exposed. The LEDs 202 are mounted to the carriersubstrate 204 by an electrically insulating bond layer 220 and ap-contact 222 is between each of the LEDs 202 and the insulating bondlayer 220. Conductive vias 224 run between the p-contact and the surfaceof the coating 218 between the LEDs 202, and respective metal pads 226run on the surface of the coating 118 between each of the posts 224 anda respective adjacent pedestal 216. This arrangement provides for aconductive path between the LEDs 202 such that the LEDs 202 areconnected in series array, with the conductive path between the LEDsisolated from the substrate by the insulating bond layer 220. Anelectrical signal applied to the metal pads runs through each of theLEDs causing them to emit light in an array. It is understood that theLED array 200 can comprise many different numbers of LEDs arranged indifferent ways, such as in a row or block, depending on the LEDs thatare interconnected by the metal pads 226.

Many different LED chips having different structures can be fabricatedaccording to the present invention. FIG. 11 shows another embodiment ofLED chips 350 according to the present invention arranged similarly tothe LED chips 10 shown in FIGS. 1 a through 1 e and described above, andfor similar features the same reference numbers are used herein. The LEDchips 350 have vertical geometry and comprise LEDs 12 each of whichcomprise an active region 14 between n-type and p-type epitaxial layers16, 18. A pedestal 28 is formed on the p-type contact 24 with a phosphorloaded binder coating 32 covering the LEDs 12. In this embodimenthowever, the LEDs 12 are on a transparent substrate 352, which allowsfor a reflective layer 354 to be formed on the substrate 352 oppositethe LEDs 12. Light from the LEDs 12 can pass through the substrate 352and reflect back from the reflective layer 354 while experiencingminimal losses. The reflective layer 354 is shown between the contact 22and the substrate 352, but it is understood that the reflective layer354 can be arranged differently, such as being the bottommost layer withthe contact 22 between the reflective layer 354 and the substrate 352.

FIG. 12 also shows another embodiment of LED chips 370 according to thepresent invention also arranged similar to the LED chips in FIGS. 1 athrough 1 e. The LED chips 370 in this embodiment have lateral geometryand comprise LEDs 12 each of which comprise an active region 14 betweenn-type and p-type epitaxial layers 16, 18. A portion of the p-type layer18 and the active region 14 is etched to reveal the n-type layer 16,with p-type contact 24 on the p-type layer 18 and the n-type contact 26on the n-type layer 16. A p-type pedestal 28 is on the p-type contact 24and n-type pedestal 30 is on the n-type contact 26. A phosphor loadedbinder coating 32 covers the LEDs 12 with the pedestals 28, 30 exposedthrough the coating 32. The LEDs 12 are on a transparent substrate 372and a reflective layer 374 included on the substrate 372 opposite theLEDs 12. The LEDs 12 have a lateral geometry with an p-type contact 24and p-type pedestal 28 on the top of each of the LEDs 12. The reflectivelayer 374 also reflects light from the LEDs with the light experiencingminimal loss through the substrate 372.

Many different variations to the LED chips can be fabricated accordingto the present invention and FIG. 13 shows another embodiment of LEDchips 400 having LEDs 402 having an active region 405 between n- andp-type layers 406, 408, on a growth substrate 404. It is understood thatthe LEDs 402 can also be provided with the growth substrate thinned orafter the growth substrate has been removed. The LEDs also have n-typeand p-type contacts 407, 409. The LEDs 402 are diced or singulated andflip-chip bonded to a submount/carrier wafer 410. Conductive traces 412are formed on the submount/carrier wafer 410 with each of the LEDs 402mounted on the traces 412, with the first trace 412 a in electricalcontact with the n-type layer 406 and the second trace 412 b in contactwith the p-type layer 408. Conventional traces can be used comprisingaluminum (Al) or Au deposited using known techniques such as sputtering.The LED 402 is mounted to the traces 412 by flip-chip bonds 413 that canbe arranged in conventional ways using known materials such as Au, orgold/tin solder bumps or stud bumps.

It is further understood that the pedestals in FIG. 13, and in theembodiments discussed above and below, can also be made of an insulatingmaterial coated by a conductive layer. In one embodiment, the pedestalscan comprise substrate material or submount/carrier wafer materiel. Forthe LED chips 400, the submount/carrier wafer can be fabricated withpedestals with each of the LEDs mounted between pedestals. A conductivelayer can be formed over the pedestals in contact with the conductivetraces or in contact with the LED using other arrangements. It isfurther understood that the pedestals can have many different shapes andsizes, and in one embodiment can comprise a reflective cup with an LEDmounted within the cup. The cup can be coated with a conductive layer incontact with the conductive traces or the LED using other arrangements.During planarization of the phosphor binder coating, the top of the cupscan be exposed for contacting. In still other embodiments, the cup canhave its own pedestals that can be exposed during planarization.

An n-type pedestal 414 is formed on the first trace 412 a and a p-typepedestal 416 is formed on the second trace 412 b, with both pedestalsbeing formed using the methods described above. A phosphor/bindercoating 418 is included over the LEDs 402, burying the pedestals 414,416. The coating 418 can then be planarized to expose the pedestals 414,416 for contacting, or in other embodiments the recesses can be formedin the coating to expose the pedestals 414, 416. The LED chips can thenbe singulated using the processes described above.

The fabrication method described in conjunction with LED chips 400allows for the use of good quality singulated LEDs 402 with the desiredemission characteristics to be selected for mounting to the wafer 404.The arrangement also allows for the mounting of LEDs 402 to the waferwith larger spaces between the LEDs 402 while not wasting valuableepitaxial material through etching of the material to form the spaces.

FIG. 14 shows still another embodiment of LED chips 500 according to thepresent invention having singulated lateral geometry LEDs 502 mounted toa carrier substrate. Each of the LEDs 502 comprises an active region 504between n- and p-type layers 506, 508, all formed successively on agrowth substrate 510. The substrate 510 can be many different materials,with the preferred substrate being a transparent material such assapphire. The LEDs 502 are singulated with at least a portion of thegrowth substrate 510 remaining.

The LEDs 502 are then mounted to a carrier substrate 512 with thesubstrate down. The carrier substrate 512 comprises a firstphosphor/binder coating 514 on a transparent substrate 516. The firstcoating 514 can be adhesive to hold the LEDs 502 or an additionaladhesive materials can be used.

A p-type contact 518 is provided on the p-type layer 508 and an n-typecontact 520 is provided on the n-type layer 506. The contacts 518, 520can comprise many different materials, with the preferred material beingreflective. By being reflective, the contacts 518, 520 reflect activeregion light making the carrier substrate 512 the primary emissionsurface. P-type pedestal 522 is formed on the p-type contact 518, andn-type pedestal 524 is formed on the n-type contact 520 as describedabove. A second phosphor/binder coating 526 is formed over the LEDs 502,burying the pedestals 522, 524. As described above, the second coating526 can then be planarized to reveal the pedestals 522, 524.

The LED chips 500 can then be singulated and this arrangement providesLED chips 500 having LEDs 502 that are surrounded by a phosphor layerprovided by the first and second coating 514, 526. The singulated LEDchips 500 can also be packaged as a conventional flip-chip device exceptwith the first and second coatings providing a white-emitting LED flipchip without further phosphor processing. This embodiment provides thefurther advantage of ability to use good quality singulated LEDs 502with the desired emission characteristics for mounting to the wafercarrier wafer 512, such that the resulting LED chips 502 are of goodquality. The LEDs 502 can also be mounted to the wafer with largerspaces between the LEDs 502 while not wasting valuable epitaxialmaterial through etching of the material to form the spaces.

FIGS. 15 a through 15 d show still another embodiment of LED chips 600according to the present invention. Referring first to FIG. 15 a, eachof the LED chips comprises LEDs 602 each of which has an active region604 between n- and p-type layers 606, 608, all formed successively on agrowth substrate 610 that is preferably a transparent material such assapphire. The LEDs 602 have a lateral geometry with a reflective n-typecontact 612 on the n-type layer 606 and a reflective p-type contact 614on the p-type layer 608. An n-type pedestal 616 is formed on the n-typecontact 612, and a p-type pedestal 618 is formed on the p-type contact614. A first phosphor/binder coating 620 is provided over the LEDs 602,initially burying the pedestals 616, 618, with coating then planarizedto reveal the pedestal.

Referring now to FIG. 15 b, trenches 622 are formed through thesubstrate 610 and partially into the coating 620, with the trenchesarranged between the LEDs 602. The trenches 622 can be formed using manydifferent methods such as by etching or cutting. Referring now to FIG.15 c, a second phosphor/binder coating 624 can be formed over the trenchside of the substrate 610, filling the trenches 622. The second coatingcan then be planarized as desired. Referring to FIG. 15 d, the LED chips600 can be singulated with the LEDs 602 being surrounded by a phosphorlayer provided by the first and second coatings 620, 624. The LED chips600 provide similar advantages as the LED chips 500 in FIG. 14, andprovides good quality flip-chip devices that can provide white lightemission without additional phosphor processing.

Referring again to FIGS. 15 a and 15 b, as an alternative to formingtrenches 622, the growth substrate 610 can be removed entirely to exposethe bottom surface of the n-type layer 606. The second phosphor/bindercoating 624 can then be formed over the exposed n-type layer, andplanarized as desired.

The present invention can also be used to cover individual LEDs insteadof those on formed in an LED chip wafer. In these embodiments, the LEDchips can be singulated and then mounted in a package or to a submountor PCB. The LED chips can then be coated and planarized according to thepresent invention to expose the pedestal(s) for contacting.

Although the present invention has been described in detail withreference to certain preferred configurations thereof, other versionsare possible. Therefore, the spirit and scope of the invention shouldnot be limited to the versions described above.

We claim:
 1. A light emitting diode (LED) chip wafer, comprising: aplurality of vertical geometry LEDs formed at the wafer level on asubstrate wafer, each LED in said plurality of LEDs comprising aplurality of semiconductor layers; a plurality of pedestals, each ofwhich is in electrical contact with one of said LEDs, said plurality ofpedestals disposed such that at least two pedestals are on one side ofeach of said LEDs; and a coating at least partially covering said LEDsand directly on the top surface of said LEDs, at least some of saidpedestals extending through and to the surface of said coating with thetop surface of said pedestals exposed at the same level as the topsurface of said coating, said coating having substantially the sameindex of refraction from the top surface of said semiconductor layers tothe top surface of said coating; wherein said coating comprises aphosphor loaded binder.
 2. The LED chip wafer of claim 1, wherein saidsubstrate wafer comprises a growth substrate wafer.
 3. The LED chipwafer of claim 2, wherein said substrate comprises a phosphor loadedbinder layer.
 4. The LED chip of claim 1, wherein said substrate waferis capable of being separated into LED chips.
 5. The LED chip wafer ofclaim 1, wherein said coating has a uniform thickness.
 6. The LED chipwafer of claim 1, wherein said coating has a total thickness variationof <50% of the average coating thickness.
 7. The LED chip wafer of claim1, wherein said coating has a textured surface.
 8. The LED chip wafer ofclaim 1, wherein said coating comprises multiple phosphors.
 9. The LEDchip wafer of claim 1, wherein said coating comprises scatteringparticles.
 10. The LED chip wafer of claim 1, wherein said bindercomprises one of the materials from the group consisting of silicone,epoxy, glass, spin-on glass, BCB, polymides and polymers.
 11. The LEDchip wafer of claim 1, wherein said phosphor comprises YAG:Ce.
 12. TheLED chip wafer of claim 1, wherein said pedestals comprise one or morestud bumps.
 13. The LED chip wafer of claim 1, wherein said LEDs aremade of materials from the Group-III nitride material system.
 14. TheLED chip wafer of claim 1, wherein said substrate wafer comprises acarrier substrate.
 15. The LED chip wafer of claim 1, wherein said LEDsare interconnected in an LED array.
 16. The LED chip wafer of claim 1, ametal pad on the surface of said coating interconnecting at least someof said exposed pedestals to form an LED array.
 17. The LED chip waferof claim 1, further comprising a reflective layer formed integral tosaid substrate wafer.
 18. The LED chip wafer of claim 1, wherein saidLEDs comprise at least a portion of a growth substrate.
 19. The LED chipwafer of claim 1, wherein said LEDs are provided on a substrate, furthercomprising trenches in said substrate and a second coating filling saidtrenches.
 20. The LED chip wafer of claim 1, wherein said coatingcomprises multiple layers with different compositions.
 21. The LED chipwafer of claim 1, further comprising the step of forming a secondcoating around at least part of said LEDs.
 22. The LED chip wafer ofclaim 21, wherein said second coating has a different composition thansaid coating.
 23. The LED chip wafer of claim 1, said LED chip wafercapable of emitting white light from said LEDs and coating.
 24. A lightemitting diode (LED) chip wafer, comprising: a plurality of verticalgeometry LEDs formed at the wafer level on a substrate wafer, each LEDin said plurality of LEDs comprising a plurality of semiconductorlayers; a plurality of pedestals, each of which is in electrical contactwith one of said LEDs, said plurality of pedestals disposed such that atleast two pedestals are on one side of each of said LEDs; and a coatingat least partially covering said LEDs and directly on the top surface ofsaid LEDs, at least some of said pedestals extending through and to thesurface of said coating with the top surface of said pedestals exposedat the same level as the top surface of said coating, said coatinghaving substantially the same index of refraction from the top surfaceof said semiconductor layers to the top surface of said coating; whereinsaid coating comprises scattering particles.